Gas chromatography (GC) is used to analyze and detect the presence of many different substances in a gaseous or vaporized sample. The function of a gas chromatograph is to separate the components of a chemical sample and detect the presence and frequently the quantity of those components. The separation is typically accomplished using a capillary column. This column is essentially a piece of fused silica tubing with a coating on the inside that interacts with the sample to separate the components. The most common type of GC column is made from fused silica and has an outside diameter that ranges from 0.700 mm to 0.350 mm.
The GC column must be mated to other components of the GC system, and the mated column must be sealed in such a way that substantially no gas can leak from the environment into the column or into the mating device or from the GC column into the environment.
Many known seals to GC columns are made by compressing a relatively soft material into an enclosed space around the column in such a manner than the material flows radially onto the column outside diameter (thus making a seal) and axially onto tapered surface of the mating device (thus making another seal). In practice, the soft material comes in the form of a ferrule and is made from either polyimide, graphite, blends of these materials, or a very soft metal. This ferrule is compressed by a nut that is rotated so that it is forced to translate axially. This pushes the ferrule along the column and into the tapered enclosed space of the mating device.
As is known, the column extends a certain distance beyond the end of the ferrule. In known GC systems, the end user sets the distance that the column extends beyond the end of the ferrule. In most GC inlets or detectors, the position of the end of the column is very important to the performance of the GC system. This position is determined by the distance of the column end from the ferrule tip. That distance is different for each inlet or detector. Mispositioning of the column by improperly setting the distance of the column end beyond the ferrule can impact the performance of the GC system.
In addition, the column must be trimmed after inserting it through the ferrule because some of the “soft” ferrule material can get into the end of the column, and contaminate the column. Other contamination may be caused from external sources (e.g., when the user's fingers unavoidably contact the ferrule and the end of the column during the installation process). This contamination can further impact the accuracy of the GC system's analysis of a sample.
Furthermore, in known GC systems, a column nut is used to secure the column to the ferrule. Human error in tightening the column nut can impact the performance of the GC column. Under-tightening of the column nut will result in ineffective sealing and the GC system will be prone to teaks. By contrast, over-tightening of the column nut can radially stress the column, causing the column to break, and thereby impacting the seal and performance of the GC system. Recent improvements in the design of soft metal seals reduces this problem, but the end of the column must still be carefully trimmed to the correct length and with a flat cut for proper performance.
What is needed, therefore, is an apparatus that overcomes at least the shortcomings of known structures described above.